docs: def _calendar_classes_for_occurrence(self, occurrence):
          """
          Return css classes to be used in admin calendar JSON
          """
          classes = [slugify(occurrence.event.polymorphic_ctype.name)]
  
          # Add a class name for the type of event.
          if occurrence.is_all_day:
              classes.append('is-all-day')
          if occurrence.is_protected_from_regeneration:
              classes.append('is-user-modified')
          if occurrence.is_cancelled:
              classes.append('is-cancelled')
  
          # if an event isn't published or does not have show_in_calendar ticked,
          # indicate that it is hidden
          if not occurrence.event.show_in_calendar:
              classes.append('do-not-show-in-calendar')
  
          # Prefix class names with "fcc-" (full calendar class).
          classes = ['fcc-%s' % class_ for class_ in classes]
  
          return classes